Effect of EPS Beads on the Behavior of Sand–EPS and Slope Stability Using Triaxial and Centrifuge Tests

The present paper is a study on the effect of expanded polystyrene (EPS) bead size on the mechanical behavior and strength parameters of Firouzkooh sand using a triaxial static apparatus. 27 triaxial (CD) tests were conducted to evaluate the effect of different factors such as EPS volumetric percentage (5%, 10%, 20%, 30%), EPS bead size, and confining pressure (100, 200, 300 kPa) on the strength parameters of the soil EPS mixture. While increasing the mixing percentage of EPS beads reduces the specific weight, the internal friction angle, the shear strength, and the initial elasticity modulus of the mixture, it increases the specimen cohesion. Specimens containing small EPS beads displayed higher internal friction angle, cohesion, shear strength, and initial elastic modulus compared with specimens containing large EPS beads. According to the results, compared with the specimens without EPS beads, a 30% addition of small and large EPS beads to the mixture increased the specimen cohesion from 0.78 to 13.8 kPa and 11.8 kPa, respectively, and reduced the friction angle by about 32% and 37%. The centrifuge tests were conducted on samples containing small EPS beads to compare the effects of the specific weight reduction and shear strength reduction parameters on the stability of the embankments. The results showed that increasing the EPS bead content increases the slip surface of failure and reduces its stability.